DESCRIPTION (Verbatim from the application): Behavioral stress is an important contributor to cardiovascular disease. The borderline hypertensive rat (BHR) is commonly used to study effects of behavioral stress on the cardiovascular system. BHR exhibit enhanced cardiovascular reactivity to acute behavioral stress and develop sustained hypertension in response to chronic stress. Previous studies by the applicant demonstrated that exposure to 10 days of air-jet stress enhanced nitric oxide synthase (NOS)-dependent relaxation of coronary and mesenteric arteries from young (3 mo. old) BHR and impaired NOSdependent relaxation in vessels from aged (18 mo old) BHR. An increase in superoxide anion production and a decrease in large Ca++-dependent K+ (BKCa) channel mediated relaxation was also observed in vessels from aged BHR. The goal of this proposal is to determine the mechanisms mediating the behavioral stress-induced changes in NOS-dependent relaxation in young and old BHR. The central hypothesis is that behavioral stress causes an increase in activity of the constitutive forms of NOS, endothelial (eNOS) and neuronal (nNOS), that is mediated by heat shock protein 90 (HSP9O), and an increase in the inducible NOS (iNOS) leading to an increase in vascular cGMP activity in coronary and mesenteric small arteries of young BHR. In old BHR, behavioral stress decreases NOS-dependent relaxation due to an increase in superoxide anions and a decrease in expression and/or function of BKCa channels. NOS-dependent relaxation of isolated microvessels, and expression, activity and localization of eNOS, nNOS, and iNOS will be determined. The role of HSP9O in enhancing NOS activity in young animals will be determined with a specific inhibitor, geldanamycin. The role of superoxide anions in impairing NOS-dependent relaxation in aged BHR will be determined by in vivo treatment with a superoxide dismutase mimetic and measurement of vascular superoxide generation. Mechanisms mediating changes in BKCa channel dependent relaxation will be determine by measuring protein expression in vascular tissue and smooth muscle cell membrane density of the BKCa channel current and single channel properties. These studies will provide new information on the mechanisms mediating stress-induced changes in NOS-dependent relaxation of coronary and mesenteric small arteries. These studies may lead to better treatment of the cardiovascular diseases associated with behavioral stress.